Cancer and Cancer Stem Cells.
A long-standing question in cancer research has been whether cancer arises through mutations in stem cells, or whether transforming differentiated cells reacquire stem cell characteristics through a process of dedifferentiation (Houghton et al., Semin Cancer Biol 4, 4, 2006; Passegue, E. Nature 442:754-7555, 2006). Tumor heterogeneity and shared features of normal stem cells and cancer cells have recently given rise to the concept of cancer stem cells (Pardal et al., Nat Rev Cancer 3:895-902, 2003; Jordan et al., N Engl J Med 355:1253-1261, 2006). However, it has been challenging to obtain firm empirical evidence supporting a normal stem cell origin of cancer and this question remained open.
Epigenetic Alterations in Cancer and Gene Silencing.
In the past decade, it has become clear that cancer arises, not only as a consequence of genetic alterations, such as mutations, deletions, amplifications and translocations, but also as a consequence of stable epigenetic changes in DNA methylation, histone modifications, and chromatin structure, with associated changes in gene expression (Jones & Laird, Nat Genet 21:163-167, 1999; Laird, P. W. Hum Mol Genet 14, R65-R76, 2005; Baylin & Ohm, Nat Rev Cancer 6:107-116, 2006; and Bird, A. Genes Dev 16, 6-21, 2002). In recent years, the disparate fields of chromatin structure, histone modification, DNA methylation, and transcription regulatory complexes have come together to provide an integrated view of epigenetics (Laird, P. W. Hum Mol Genet 14, R65-R76, 2005; Ordway & Curran, T. Cell Growth Differ 13:149-162, 2002; Freiman & Tjian Cell 112, 11-17, 2003; Felsenfeld & Groudine, Nature 421; 448-453, 2003; and Jaenisch & Bird, Nat Genet 33:245-254, 2003). This elaborate mechanism for regulating areas of the genome for transcriptional activity, repression, or silencing participates in mammalian development (Li et al., Cell 69:915-926, 1992), genomic imprinting (Li et al., Nature 366:362-5, 1993), X-inactivation in females (Zuccotti & Monk, Nat Genet 9:316-320, 1995; and Boumil et al., T. Mol Cell Biol 26:2109-2117, 2006), in silencing parasitic DNA elements (Walsh & Bestor, Genes Dev 13:26-34, 1999), and in coordinating cell-type specific gene expression (Futscher et al. Nat Genet 31:175-179. 2002).
Cancer cells contain extensive aberrant epigenetic alterations, including promoter CpG island DNA hypermethylation and associated alterations in histone modifications and chromatin structure. Aberrant epigenetic silencing of tumor-suppressor genes in cancer involves changes in gene expression, chromatin structure, histone modifications and cytosine-5 DNA methylation.
Epigenetic Mechanisms in Embryonic Stem (ES) Cell Differentiation).
Embryonic stem cells are unique in the ability to maintain pluripotency over significant periods in culture, making them leading candidates for use in cell therapy. Embryonic stem (ES) cell differentiation involves epigenetic mechanisms to control lineage-specific gene expression patterns. ES cells rely on Polycomb group (PcG) proteins to reversibly repress genes required for differentiation, promoting ES cell self-renewal potential. ES cell-based therapies hold great promise for the treatment of many currently intractable heritable, traumatic, and degenerative disorders. However, these therapeutic strategies inevitably involve the introduction of human cells that have been maintained, manipulated, and/or differentiated ex vivo to provide the desired precursor cells (e.g., somatic stem cells, etc.), raising the specter that aberrant or rogue cells (e.g., cancer cells or cells predisposed to cancer that may occur during such manipulations and differentiation protocols) may be administered along with desired cells.
Therefore, there is a pronounced need in the art for novel, effective and efficient methods for stem cell and/or precursor cell monitoring and validation, and for novel therapeutic methods, comprising monitoring and/or validating stem cells and/or precursor cells prior to therapeutic administration to preclude introduction of aberrant or rogue cells (e.g., cancer cells or cells predisposed to cancer).
Ovarian Cancer. In the US and Europe, epithelial ovarian cancer causes more deaths than cancer in any other female reproductive organ. It is estimated that there are about 20,180 new cases of ovarian cancer and 15,310 deaths in the US per year (1). Due to the current lack of early detection strategies, many ovarian cancer patients present with advanced stage disease, and the overall 5-year survival for these women is less than 30% (2). Despite the development of new therapeutic approaches, these survival statistics have remained largely unchanged for the past three decades. The most important prognostic parameters for this disease are age, stage, grade and optimal cytoreductive surgery (where all visible cancer in the peritoneal cavity is removed). Beside molecular genetic changes and expression profiling, studies have also begun addressing the epigenetic components of ovarian carcinogenesis (3-5). Changes in DNA methylation status (predominantly at CpG) are among the most common molecular alterations in human neoplasia (6). DNA methylation changes promise to be important screening markers for carcinogenesis.
Therefore, there is a pronounced need in the art for a better understanding of the molecular pathogenesis of ovarian cancer and identification of new drug targets or biomarkers that facilitate early detection.
Breast Cancer.
Breast cancer is the most frequent malignancy among women in the industrialized world. To date the presence or absence of metastatic involvement in the axillary lymph nodes is still the most powerful prognostic factor available for patients with primary breast cancer (1), although this is just an indirect measure reflecting the tendency of the tumor to spread. Chemotherapy can be an integral component of the adjuvant management strategy for women with early-stage breast cancer. Recently applicants showed that RASSF1A DNA methylation in serum is a poor prognostic marker in women with breast cancer (2) and that this cancer-specific DNA alteration allows monitoring of adjuvant Tamoxifen therapy, which is applied mainly in ER positive tumors (3). To date, however, no tool is available to sufficiently predict or monitor efficacy of neoadjuvant or adjuvant systemic chemotherapy which is frequently applied in ER negative breast cancer. Therefore, there is a pronounced need in the art for a better understanding of the molecular pathogenesis of breast cancer and identification of new biomarkers that facilitate early detection and treatment of breast cancer (e.g., ER negative breast cancer).